What is a metroidvania?
A metroidvania is a combination of the gameplay style of Metroid's exploration and mechanics with the gothic style of the castlevania series, add in a few RPG elements and you have a Metroidvania!
An idea started by industry legend, Koji "IGA" Igarashi, the first metroidvania Castlevania: Symphony of the Night became a huge cult classic and earned a following that would expand the genre in many ways. From combo points featured in games like An Elysian Tail to rogue-like qualities like Rogue Legacy the genre has become a very popular trend in both handheld and indie crowds.
https://en.wikipedia.org/wiki/Metroidvania